On Thursday, the communist country fired four short-range missiles from its southeast coast into the East Sea, throwing cold water on a recent thaw in inter-Korean relations.

"Given its timing, we believe that the North's missile launch was very intentional and a kind of provocation," Seoul's defense ministry spokesman Kim Min-seok said in a regular briefing.

Noting that the government believes what the North fired "were Scud type ones," he said Pyongyang "made the plan deliberately" to resist the joint military exercises between South Korea and the United States that kicked off on Monday.

The North had called for their cancellation, claiming that they are a rehearsal for a war against it.

Thursday's launch was the North's first firing of a Scud missile since 2009, which "poses a threat to South Korea as the whole Korean Peninsula is in range," he added.

The communist country has three types of Scud missiles -- the Scud B with a range of 300 kilometers, the Scud C with a range of 500 km and the Scud D with a range of 700 km.

On the first day of the drills, North Korea briefly violated the tense western sea border three times, following last week's firing of what military sources believed to be a new type of rocket larger than 300 mm caliber from a multiple rocket launcher.

Though the defense ministry spokesman said no signs of additional missile launches or other types of provocation have been detected, sources here said the North has banned its fishing boats from operating in the East and Yellow Sea, and put its troops in the border region on "special alert."

"Since earlier this week when the military drills began, the North has kept its ground and naval forces in the border regions on special alert," a senior government source said, requesting anonymity.

"We also can see the North's reinforcement of artillery exercises in response to the joint drills."

Another military source also speculated that "chances are that the North would provoke further given that the authorities have controlled fishing boats in the East and Yellow Sea border regions."

The missile launch also came at a time when the inter-Korean ties have been showing signs of improvement. Following the rare high-level inter-Korean talks, the two sides held reunions of families separated since the Korean War for six days from Feb. 20, for the first time since 2010.

Still, the South Korean government expressed hope that the North's latest missile launch won't affect inter-Korea relations and Seoul's move to hold further reunions.

"We expect family reunions and inter-Korean relations to fare well down the road," without being affected by the missile launches, said Kim Eui-do, the spokesman for the unification ministry in charge of inter-Korean relations.